1. Field of the Invention
The present invention relates to an image blur correction apparatus for effecting image blur correction in a lens barrel or the like.
2. Description of the Related Art
Conventionally, as an apparatus for preventing image blur due to hand-shake or the like, which is likely to occur in hand-held photography or the like, there has been known an image blur correction apparatus which detects the shake condition of a camera by a shake detector and which shifts a correction lens in a direction orthogonal to an optical axis in accordance with the detection.
In a camera provided with an image blur correction apparatus, a correction lens constituting at least a part of a photography lens system is movably supported.
By moving this correction lens in a plane orthogonal to the optical axis of the principal optical system so as to compensate shaking, deviation of the imaging position due to shaking is corrected, thereby eliminating image blur.
A problem with this image blur correction apparatus is the adverse influence due to rotation of a movable member, which movably supports the correction lens for image blur prevention, in a plane orthogonal to the optical axis of the movable member.
Generally speaking, a center of gravity of the movable member is at a position deviated from the axis of a direction of a driving force generated by a drive unit for moving the movable member. Therefore, at the time of image blur correction, a rotational moment which causes the movable member to rotate in a plane orthogonal to the optical axis is generated by the driving force.
Further, a force causing the movable member to rotate is also generated by phenomena other than the driving force such as vibration and friction.
Thus, without a unit for suppressing rotation of the movable member within a plane orthogonal to the optical axis, the movable member would be allowed to freely rotate during the image blur correction operation, to thereby come into contact with a fixed member. Thus, there is a danger of the driving characteristics being changed or the image being disturbed.
A position detection sensor of the image blur correction apparatus is formed of a combination of a magnet and a magnetic sensor, a combination of a light emitter and a light receiving element, or the like.
In such a position detection sensor, it is assumed that the correction lens moves, in a plane perpendicular to the optical axis, in one direction: a yaw direction which is a horizontal direction in a plane perpendicular to the optical axis in a posture of camera or the like in use, or a pitch direction which is a vertical direction in a plane perpendicular to the optical axis in the posture of camera or the like in use.
Thus, when the correction lens rotates to a large degree, the output characteristics of the position detection sensor undergo a change to make it impossible to perform accurate position detection, generating so-called cross talk.
Further, when the position detection changes due to the rotation, there is also generated oscillation in feedback position control, which further leads to deterioration in the optical performance at the time of hand-shake correction.
As a measure for suppressing rotation of the movable member about the optical axis, there has been proposed an image blur correction apparatus in which a correction lens held by the movable member is displaced in the yaw direction or the pitch direction without being rotated about the optical axis.
For example, Japanese Patent No. 3229899 discloses an image blur correction apparatus provided with a guide shaft for regulating rotation, and Japanese Patent Application Laid-Open No. H06-242485 discloses an image blur correction apparatus in which there is further provided a drive unit for suppressing rotation for the purpose of regulating rotation.
In the configuration of Japanese Patent No. 3229899, in order to allow the correction lens to move in the yaw direction and the pitch direction, which are two axial directions orthogonal to each other within the same plane, there is adopted a gimbal structure in which the correction lens is guided and held by two guide shafts.
In order to correct image blur, a response to a frequency band of up to several tens Hz is necessary, and the positional accuracy must be controlled with high precision, and hence retention relatively free from friction and backlash is indispensable.
Thus, in the construction of Japanese Patent No. 3229899, double fitting is required for the two guide shafts to accurately displace the correction lens in the same plane.
It is rather difficult to maintain such double fitting with high precision without involving any backlash. In reality, adjustment, etc. are required, resulting in a rather high cost.
Further, in this construction, rotational moment causing the movable member to rotate is allowed to remain, and hence, when the movable member is displaced, a twisting force is generated between the guide shafts and a bearing provided in a movement frame, and a deterioration in minute amplitude characteristics occurs as a result of the influence of friction due to this twisting force.
In the construction of Japanese Patent Application Laid-Open No. H06-242485, there is provided a drive unit for suppressing rotation about the optical axis in addition to the drive unit for driving the correction lens in the yaw and pitch directions.
In this case, it is possible to achieve an improvement in terms of deterioration in minute amplitude characteristics due to friction in the mechanism as in the case of Japanese Patent No. 3229899. However, the provision of another drive unit leads to complicated control, and increases in power consumption, in the number of parts, in assembly man-hours, and in cost.
Due to the recent progress in the semiconductor fine processing technology, in an image pickup element such a CCD or CMOS, which converts an object image formed in a focal plane by a photography optical system into an electric signal, it has become possible to produce image pickup elements of smaller pixel pitch.
As a result, there have been generated the following two tendencies: a further downsizing of the optical system through preparation of as many pixels as in the prior art in a smaller area, and a further enhancement in the resolution of the optical system due to an increase in the number of pixels in the same area or through an increase in area.
In the former, the moving amount of a shift lens unit for the correction of hand-shake of the same amount is substantially proportional to the image pickup area, and hence a still finer movement is required, and a movement of still higher precision is required.